THIS invention relates to a composite diamond window.
There is a requirement in high power radiation sources, such as laser, synchrotron, RF or X-ray sources, for windows or viewports which are transparent to the radiation and able to withstand substantial pressure differentials across them. It has been proposed to make the required window out of diamond because of the high radiation transparency, high thermal conductivity, low expansion coefficient and low power absorption of diamond.
In the window construction, the window is generally mounted in sealed manner to a metal substrate or frame. It is however recognised that the initial high temperature bakeout of the radiation source and subsequent thermal cycling thereof will give rise to a substantial thermal mismatch between the diamond and the metal frame, particularly where the diamond is relatively thin, which may degrade the seal. In attempts to counter this problem, it has been proposed to mount a CVD diamond (i.e. diamond formed by chemical vapour deposition) window to its metal frame, typically of copper or stainless steel, by means of liquid solders, metal brazes and diffusion bonds. Such attempts have however been unsuccessful in view of the high stresses caused by the large thermal expansion mismatch between the diamond and metal.
The applicant's co-pending British patent application 9920384.6 filed on Aug. 28, 1999 and entitled “Joining of CVD Diamond Bodies to Metal Structures” proposes that a CVD diamond window be mounted to a metal frame via an intermediate ceramic body, typically of silica. The diamond window is bonded to the intermediate body and the intermediate body is, bonded to the metal. This has the advantage that the ceramic can have thermal expansion characteristics which are compatible with those of the diamond, thereby reducing the severity of the thermal mismatch between the diamond and metal.